Wasatch Weather Weenies

A Great Storm in Utah is something we are all waiting for but is also an essay that John Muir wrote while visiting the Salt Lake Valley in 1877.  The essay was sent to me by a former student, Matt Jeglum, who knows how much I enjoy this sort of weather and nostalgia, and contained within Muir's book Wilderness Essays . In the essay, Muir describes a storm on May 19, 1877.  The date is very close to the peak time of year for strong cold fronts in northern Utah and he was impressed. "Utah has just been blessed with one of the grandest storms I have ever beheld this side of the Sierra.  The mountains are laden with frsh snow; wild streams are swelling and booming adown the cañons, and out in the valley of the Jordan a thousand rain-pools are gleaming in the sun."  But before describing the storm, he provides some great observations of Utah snow and weather.  First, he suggests a late start to the snow season with snow piling up in the spring. "In all the upper caño...

It will take a while to get here, but a bonafide trough will be coming to Utah for the weekend. Before that, we're going to be in the so-called warm-before-the-storm (in this case a dry frontal passage with dust) with a ridge building over Utah today. The ridge will be followed by the development of warm southwesterly flow ahead of the trough later in the week, as illustrated by the GFS forecast below for 0000 UTC 21 June (6 PM MDT Friday). Although yesterday's high was "only" 87 and this morning was pleasant, our July like weather returns for the rest of the work week with NWS forecast highs for the Salt Lake City airport of 92 today, 102 Thursday, and 96 on Friday.  Critical fire weather conditions will be in place for much of this period. Saturday is a transition day with the front forecast to be moving over northern Utah at 0000 UTC 22 June (6 PM MDT Saturday).   Depending on your location and exposure, this looks like a recipe for dust Friday and Saturday in both...

 As I type this on Sunday afternoon (June 1), the temperature at the Salt Lake City International Airport is about 92°F at 2 PM.  The record for the day is 94°F, so we have a solid shot at tying or eclipsing that.  A high of 94 is also consistent with the average high for July 11, so we're getting a too early taste of mid summer.   Fortunately a weak cold front is coming through tomorrow morning.  Tomorrow afternoon will be more pleasant than today with cooler, drier, northwesterly flow.   Right now it's looking like the frontal passage will probably be a dry one in Salt Lake.  The NWS forecasts give us the not quite zero possibility of a shower or thunderstorm: "A slight chance of showers and thunderstorms before midnight, then a slight chance of showers between midnight and 3am." Hopefully we see something, although my expectations are for nothing.  At least it will be cooler tomorrow.  

It's always exciting in the dog days of summer to see a trough embedded in the midlatitude westerlies pay a visit to Utah. The GFS forecast below shows the trough moving through Utah at 1800 UTC (1200 MDT) August 8 (today).  At 700 mb there is even...wait for it...a temperature gradient with cold air advection (i.e., the transport of cold air into the area).   It's difficult to find evidence of a well-developed front at the surface, but there is evidence of some enhanced northerly or northwesterly flow over the west desert and along portions of the northern Wasatch Front at around 8 AM this morning.  Winds in the Salt Lake Valley, which are often southerly or southeasterly in the morning if there's no large scale forcing, show a bit more disorganized character.    That could reflect some of the showers that moved through, but also the fact that the surface trough is nearby or just downstream.   The NWS forecast for today calls for scattered shower...

You can't stop Mother Nature this season.  More insane numbers from the Wasatch.  As reported by the Utah Avalanche Center this morning, storm totals for the PC Ridgline are now .95–1.05" water and 15–22" of snow and Upper Cottonwoods 1–2.5" of water and 16–35" of snow.  The Ogden and Provo area Mountains have also been blessed with big dumps.  Snowfall late yesterday was intense at Alta-Collins. Hourly snow interval observations show an increase in snow depth from 3 to 10 inches in two hours from 5 to 7 PM.  Normally the board is wiped between 4 and 5 PM, but I can't tell if that was done as the interval remained at 3 inches.  Given the intense snowfall rates, it is possible it was wiped and it basically was snowing 3" an hour starting at about 4 PM.    I've heard that the Cottonwoods were a mess during this period and that the overnight road closure was moved up to 8 PM.  If so, I suspect both were closely related to the heavy snowfall....

Super excited for the events to unfold later today through Wednesday.  The models continue to be on track with a major, all elevations snow event for Utah.   The large-scale setup for this event is an amplifying upper-level trough that digs southward along the Pacific Coast.  As discussed in an earlier post , this amplifying system is actually connected to the development of two powerful cyclones over the northwest Pacific, which amplify the immediate downstream ridge over Alaska, which in turn amplifies the trough along the Pacific Coast through a process known as downstream development.  The GFS forecast valid at 0000 UTC 22 February (5 PM MST Tuesday) shows all of these features nicely with the northwest Pacific cyclones marked with Ls, the ridge with a zig-zagged line, and the trough with a dashed line.   This is a highly dynamic situation with rapid amplification of the jet-stream pattern.  It is only through the power of numerical weather pr...

Forecasts for the weekend storm are pretty locked in and I think there's about a 50% chance that there will be enough snow to ski at Alta on Monday.   For that forecast, I'm assuming that 2" of snowfall water equivalent (SWE) is the minimum needed for skiing the main run down Collins Gulch.  Some might go with less than that, but historically that's my bare minimum.  As discussed previously, the remainder of the work week looks dry and pleasant.  The 0600 UTC initialized GFS brings the much anticipated cold front into Utah during the day on Saturday and at 0000 UTC 23 October (6 PM MDT Saturday) widespread frontal precipitation covers the Salt Lake Valley and central and northern Wasatch.   It's a slow moving frontal system and by 1200 UTC 23 October (6 AM MDT Sunday), the 700-mb (roughly 10,000 ft) trough axis has only progressed into central Utah.  If we are fortunate, this will give us several hours of frontal precipitation. During the day on S...

This isn't exactly breaking news, but change is coming in the form of a cold front this weekend.   Until then, we will have a splendid run of dry, fall weather.  Ideal for mountain biking or hiking if you can get out.  The situation this morning is characterized by a strong, high-amplitude ridge centered over central Idaho.   This ridge will weaken during the work week, but we should see mainly sunny weather through at least Thursday.  On Friday, there may be a few high clouds, but no biggie. During the weekend, an upper-level trough digs into the western United States.  The latest GFS forecast below shows the associated cold front over northern Utah at 0000 UTC 23 October (6 PM MDT Saturday).   The GFS time height section shows very low humidities over Utah and wonderful fall weather through Friday morning (a reminder that time increases to the left in the plot below).  Some higher humidity air moves in aloft ahead of the front whi...

There aren't many days when the Avenues get the bragging rights for snowfall, but today is one of them.   During the day yesterday, a frontal boundary developed over northern Utah, with the band especially strong along the I-80 corridor from the area near Stansbury Island to the Salt Lake City International Airport and the lower avenues.  Below is the radar imagery for 02:42 UTC (7:42 PM MST) illustrating the situation.   Source: NCAR/RAL A sounding collected at the airport at just before 0000 UTC (5 PM) showed shallow northerly flow associated with the front below about 725 mb, with southeasterly flow aloft.   Source: SPC Additionally, the sounding was very moist at low levels and near what meteorologists call moist neutral , meaning that the stability was weak to non-existent or even weakly unstable for moist flows (i.e., with a relative humidity of 100%).  Thunder was even reported in some parts of the Salt Lake Valley that afternoon. ...

  After fits and starts overnight with convective graupel showers, full-blown frontal precipitation has developed over northern Utah this morning and mountain snowfall rates have really gone through the roof.  Observations from Alta-Collins show .09" of water equivalent and less than an inch of snow through 5 AM, but since then, there's been 0.29" of water equivalent and about 4" of snow.   Radar at 1433 UTC (0733 MST) shows pretty complete coverage over the northern part of the state.  There are a few holes of lighter precipitation, but for the most part, this is as good as it gets for complete coverage in this part of the world.   In the upper aves, we were just starting to turn to snow at 7:15 AM with trace accumulations on colder surfaces.  This puts the snow level pretty much at 5,000 feet.   When I got to campus, it was mainly rain with a few flakes mixed in.   To the north, a look at UDOT cameras shows accumulating snow ...

It's a somewhat surprisingly complicated weather forecast for the weekend, but not that atypical for September as we transition from the so-called monsoonal flow pattern to the cool-season westerly storm track.  We'll begin with a look at the GFS forecast valid 0600 UTC 18 September (0000 MDT Saturday).  At this time, a deep upper-level trough (black contours) and frontal system are pushing onto the northwest coast.  Ahead of this system is a much weaker trough over California.  It doesn't look like much, but it contributes to a surge of monsoon moisture (color contours are precipitable water – a measure of the total atmospheric water vapor) into Utah (red arrow).   As the deep upper level trough and cold front push into the Pacific Northwest, the weak trough slowly moves northeastward and the monsoon moisture streams into northern Utah.  By 1800 UTC 18 September (1200 MDT Saturday) the GFS is generating some scattered precipitation in northern Utah, m...